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t As noted from the table, in the months of January, February, March, November and December, deep percolation probably will occur. During these months, it is critical.that nitrogen not be applied to lawns and landscaping, not only because of deep percolation,but also since most plants are in dormancy and there will be little uptake. In addition, if the leachlines can be installed as high in elevation as possible, during the months of April through October, significant evapotranspiration may occur to alleviate excessive percolation of septic effluent. This premise would not only apply to surface and subsurface soil temperatures causing evaporation, but also to transpiration by certain plants that are planted near, or over the leachfield. These would include grasses and shallow rooted shrubs over the leachfield. C. GROUNDWATER INFORMATION L. ESTIMATED GROUNDWATER GRADIENT AND VELOCITY According to the most recent Groundwater Lines of Equal Depth Map (1999) provided by the San Joaquin County Flood Control District, the static water level under the center of the project is approximately 140 ft below grade.. Lines of Equal Elevation maps are included in Appendix 6 to illustrate the groundwater directional flow during the years of 1992, 1996, 1997, 1998, and 1999. As noted the directional flow appears to have changed over these years, but is predominately toward the Mokelumne River. Whether the gradient under the subject property flows northwesterly toward the River, or if it continues in a westerly direction to eventually encounter the River is unknown without highly sophisticated monitoring over time. Groundwater typically follows the topography of the land surface. Consequently, as denoted from the USGS topographical map, the flow direction may be in a predominate westerly direction until the influence of the River overtakes gravitational flow. The equal lines map show the gradient to be very gradual and flat as the groundwater flow travels west-southwest toward the town of Lockeford. The groundwater gradient as the flow descends from the project site is estimated to be 10 ft 7,920 ft (1.5 mi) = 0.00126 ft/ft, based on the equal elevation and depth maps. The velocity of the groundwater directly downgradient from the subject site can be estimated by the following formula: K (h, h2) Vaquifer L 7.5 p 3, Where: K=Hydraulic conductivity of aquifer formation in gals/day/ft, 5000 gals/day/ft2 (est. based on a silty, { medium sand formation) h,= 140 ft h,= 130 ft �i L-= 1.5 mi =7,920 ft p =porosity of aquifer 37% (est) i. Vnquif,=2.3 ft/day -- - { ' Page -8- Chesney Consulting